1. Field of the Invention
The present invention relates to a semiconductor mounting package for mounting one or a plurality of high power semiconductor chips such as high power transistors and microwave monolithic ICs (MMIC).
2. Description of the Background Art
As output power and operation frequency of a semiconductor chip have been improved, amount of heat generated from the semiconductor chip has been increasing. Further, there is a strong demand in the market to reduce the size and weight of electronic equipments, and therefore packaging density of semiconductor chips has been made higher and higher. Therefore, devices mounting semiconductor chips have been required to satisfy severe conditions of heat radiating characteristic.
In a device of which heat radiating characteristic is required, a material having high thermal conductivity is used as a heat sink to form a substrate, the semiconductor chip is mounted thereon, and heat generated from the semiconductor chip is effectively diffused to prevent overheating of the semiconductor device.
Conventionally, AlN (aluminum nitride) and BeO (beryllium oxide) have been widely used as materials of the heat sink. BeO is disadvantageous in that it has an insufficient heat radiation characteristic and poor machinability, as well as strong toxicity. Though AlN is not toxic, its heat radiation characteristic is poor, and therefore it is not a satisfactory substitute for BeO.
Japanese Patent Laying-Open No. 7-99268 discloses a ceramic package having improved heat radiation characteristic, by adhering a Cu plate on a BeO or AlN substrate. It has been difficult, however, to ensure sufficient heat radiation even by this ceramic package.
Among substances, diamond has the highest thermal conductivity, and hence it is an ideal material to be used as a substrate for the semiconductor chip to lower heat resistance of the device mounting the semiconductor chips such as described above. The problem is that diamond is too expensive for this use.
Chemical vapor deposited diamond which has been under development recently is advantageous in that it allows synthesis over a large area as compared with natural diamond or diamond grown by high pressure and high temperature method and that it is inexpensive. Coefficient of thermal expansion of chemical vapor deposited diamond, however, is smaller than that of the semiconductor chips to be mounted on the substrate formed of the chemical vapor deposited diamond, leading to a problem that after the semiconductor chips are mounted by brazing on the substrate formed of the chemical vapor deposited diamond, the chip cracks.
In view of the foregoing, the inventors of the present invention have proposed in Japanese Patent Application No. 10-6238 (filed on Jan. 16, 1998), a heat spreader in which a substrate of Si (silicon), SiC (silicon carbide) or AlN (aluminum nitride) is coated with thin diamond. The heat spreader two-dimensionally diffuses heat generated film the semiconductor chips through the thin film of diamond, whereby the heat can be dissipated. Further, as the diamond is formed in the form of a thin film, manufacturing cost of diamond is low and effective coefficient of thermal expansion at the surface of the diamond increases, which prevents destruction of the chip at the time of brazing of the semiconductor chips.